1. Field of the Invention
The present invention relates to a coil spring compressor which is used in the assembly of subassemblies of automotive front or rear suspension systems, in particular, MacPherson type suspension systems.
2. Description of the Prior Art
Certain types of automotive suspension system such as of the MacPherson type comprise a suspension subassembly. The subassembly includes a strut formed by a lower tube. The strut includes a built-in shock absorber. A part of a piston of the shock absorber projects upward from the strut in a telescoping fashion. A coil spring is mounted in a compressed state around the strut between a lower spring seat integral with the strut and an upper spring seat fastened to the upper end of the piston of the shock absorber. Such a suspension subassembly is assembled separately and then mounted as a unit in a vehicle body.
During the assembly of a MacPherson type suspension subassembly, the coil spring is passed from above around the stanchion with its lower end abutting against the lower spring seat. The coil spring is then compressed by a suitable power tool to bring the upper end of the coil spring below the upper end of the piston of the shock absorber, so that the piston upper end protrudes beyond the coil spring upper end. The upper spring seat is then fastened to a threaded part of the upper end of the shock absorber piston by a nut through an upper support. As a result, the coil spring is retained between the upper and lower spring seats in a compressed state.
Japanese Unexamined Utility Model Publication (Kokai) No. 56-109826 and Japanese Unexamined patent publication (Kokai) No. 57-1630 disclose a type of device for compressing the coil spring for the above-mentioned purposes. Such a coil spring compressor comprises a movable head plate positioned above a base. The head plate is mounted on the top of a vertically slidable drive shaft which is driven upward and downward by a rotary drive mounted on the base and driven by a motor through a clutch. The vertical movement of the head plate is guided by a pair of slide bars connected thereto and slidingly received within a pair of guide blocks secured to the base. The head plate is provided with a spring compressing mechanism having a plurality of push-down fingers (or hooks) which are adapted to push the coil spring down thereby to compress the coil spring and which are designed to protract toward and retract from the coil spring mounted on the MacPherson strut. When the head plate is moved downward for a predetermined distance with the push-down fingers engaging the coil spring, the coil spring is compressed to a desired degree allowing the operator to fasten a nut to retain the upper spring seat. Normally, the push-down fingers, which will be referred to merely as fingers hereinafter, should be so positioned that they engage between the first and second turns of the coil spring to permit the upper spring seat to be placed on the upper free end of the spring. The length and pitch of a coil spring in its free relaxed position vary according to the particular suspension system to be assembled. Thus, the vertical positions of the fingers must be adjusted depending on the particular coil spring used. Failure to adjust the position would cause the upper end of the coil spring to be eccentric or inclined with respect to the longitudinal axis of the shock absorber, resulting in a relative positional deflection between the coil spring and the upper spring seat.
Japanese Unexamined patent publication No. 57-1630 discloses a position adjusting means comprising a plurality of limit switches. Japanese Unexamined Utility Model Publication No. 56-109826 discloses an adjusting mechanism employing cam mechanisms. The limit-switch adjusting mechanism is disadvantageous in that it entails a large number of limit switch positions in order accommodate coil springs of various sizes and that the positions of the limit switches must be altered each time the size of the coil spring is changed. Moreover, the electric circuit connecting the limit switches is complicated, making the maintenance thereof troublesome. The cam-mechanism adjusting mechanism suffers from similar disadvantages and, in some cases, requires alteration of the cam profile.
In the copending patent application Ser. No. 453,839 filed Dec. 28, 1982, and assigned to the assignee of the present invention, there is disclosed a coil spring compressor suitably used for compressing a coil spring during the assembly of MacPherson type suspension subassemblies. This coil spring compressor comprises a base, a movable head plate positioned above the base for translational movement thereto, and means for driving the head plate toward and away from the base. The head plate is provided with a pair of spaced guide bars connected thereto and suspended therefrom. A carriage is mounted on the guide bars for vertical sliding movement through a predetermined distance. The carriage is provided with a frontal opening having a sufficient size to receive therethrough without interference a coil spring to be compressed. The carriage is provided with four compressor arms, each of which is pivoted at an end to the carriage and is provided at the other end with a push-down finger (or hook) projecting toward and engageable with any selected turn of the coil spring. The four compressor arms are grouped into two pairs, one of which is arranged along one side of the frontal opening of the carriage and the other along the opposite side. The front and rear compressor arms in each pair are interlocked with each other so that when the front arm in each pair is rotated toward and away from the coil spring, the rear arm swings conjointly with the front arm toward and away from the coil spring. The front arm in each pair is provided with an operating handle. In use, the operator first slides the carriage upward and downward along the guide bars and adjusts the vertical position of the carriage so that the fingers or hooks are leveled between the desired successive turns of the coil spring, normally between the first and second turns. Then, the operator closes the handle together to insert the hooks between the selected turns of the coil spring and turns on the drive means to lower the head plate. As the head plate travels downward, the hooks are urged against the second turn of the spring and compress the same to the desired degree.
In the coil spring compressor of the type described, however, the vertical positions of the push-down fingers or hooks cannot be independently adjusted. In other words, the fingers are immovably secured to the corresponding compressor arms and, accordingly, it is impossible to independently adjust the vertical positions of the fingers in each pair. Therefore, even if one of the fingers does not come into contact with the coil spring when the fingers are brought into engagement with the coil spring to compress the latter, no adjustment of the vertical position of the finger in question can be effected. This will result in the coil spring being off center with respect to the strut.